1. Field of the Invention
The present invention relates to a package, more particularly to a mold package which seals a chip mounting an ultra high frequency semiconductor, an optical element, a surface elastic wave element, a resonator, or the like.
2. Description of the Related Art
In an ultra high frequency device, when a size of its package becomes larger, an inductance component of a lead becomes larger, whereby a loss in a high frequency becomes larger. Therefore, the ultra high frequency device must be housed in a package which is as small as about 2 mm diameter. Furthermore, the ultra high frequency device has been heretofore incorporated in a ceramic hollow package. However, the ceramic package is high in cost so that the ultra high frequency device has a tendency to be incorporated in a resin mold package.
Since resin has a high dielectric constant, a parasitic capacitance becomes high when the whole of the device is sealed by resin. A high frequency gain of the device can not be obtained. To solve such a problem, a resin mold package in which a space is provided on a surface of the device has been proposed.
For example, in a gazette No. WO94/17552, disclosed is a high frequency plastic package having a structure that a semiconductor chip is mounted on a lead frame, a substrate portion made of resin mounting the lead frame on its surface is covered with a plastic cap, whereby the semiconductor chip is sealed. Furthermore, in Japanese Patent Application Laid Open No. Heisei 2-25057, disclosed is a method of manufacturing a semiconductor device wherein after molding a resin case having an opening at its upper portion integrally with a lead frame having an inner lead portion at its inner bottom, the inner lead portion and a semiconductor chip are connected to each other, and a cover for sealing the semiconductor chip is adhered to the resin case.
Furthermore, in Japanese Patent Application Laid Open No. Heisei 5-291319, disclosed is a semiconductor device wherein a pad of a semiconductor chip and a metal foil are connected through a connection projecting electrode, the metal foil being formed on a flexible film substrate, a frame-shaped dam pattern is formed either outside the projecting electrode or inside it, and by interposing the semiconductor chip and the flexible film substrate using a resin sheet for sealing, both of the chip and the substrate are integrally fixed to each other. In Japanese Utility Model Application Laid Open No. Showa 62-135441, disclosed is a flip chip mounting structure wherein a flip chip having a solder bump formed thereon is connected onto a substrate provided with a plurality of electrodes thereon, and a space having a height equal to the solder bump is formed between the substrate and the flip chip by dropping resin onto the flip chip from a direction above the flip chip.
However, in the high frequency plastic package disclosed in the WO94/17552 gazette, since a bending working for the lead frame is conducted after sealing the plastic cap, there are problems that due to stress applied at the lead frame bending working, the lead frame moves over the mold, the plastic cap is cracked, or an adhered portion is peeled off whereby the plastic cap is detached.
On the other hand, in the manufacturing method of the semiconductor device disclosed in the Japanese Patent Application Laid Open No. Heisei 2-25057, an outer periphery of the opening serves as a frame portion, and the lead frame is held between a base portion and a frame portion. Therefore, the above-described problems hardly occur. However, in general, electronic parts are initially mounted at a specified position of a printed circuit board and the like by a handler of a mounting machine and is soldered to the printed circuit board. Further, the printed board is partially sealed with a sealing case or the printed circuit board is attached to a case of a body.
During these processes, a portion of the handler, the sealing case, or a driver sometimes touches inadvertently the package which has been already mounted on the substrate. In the case of a comparatively large package, it is possible to form the frame so as to have a thick thickness, so that the package is never broken when the handler and the like touches the package.
However, in a case of packages for a ultra high frequency device, since its diameter is about 2 mm, a thickness of the frame is as small as about 0.5 mm. Therefore, with an application of a slight shearing stress in a lateral direction to the package, there is a possibility of breakdown of the package.
In the semiconductor device disclosed in the Japanese Patent Application Laid Open No. Heisei 5-291319, since the flexible film or the resin sheet is used as a main body, there is a problem that the package itself has a poor mechanical strength. Furthermore, the package is distorted by an application of pressure at sealing, and there is a possibility that resin flows into the inside of the package from a small space of the dam pattern, thereby reducing reliability of the device. In the mounting structure disclosed in the Japanese Utility Model Application Laid Open No. howa 62-135441, the dropped resin spreads into the periphery of the semiconductor chip, so that a problem of flowing of the resin still remains. Furthermore, unless optimization for a viscosity of the resin and for a space between the substrate and the semiconductor chip are done, the space between the substrate and the semiconductor chip is not always formed.